With the advancement of high performance computers, the quantity of information to be processed including image data is continuously increasing. Accordingly, a larger storage capacity is required for a magnetic recording disk drive which is employed as an external storage device. Presently, a storage capacity as large as several hundred megabits per square inch has been realized. A magnetic head, used in such a high density magnetic recording disk drive, is an integrated head having a separately provided electromagnetic induction head for use as a recording head and a magnetoresistive head for use as a read-back head. The magnetoresistive head has improved read-back sensitivity as compared with the conventional electromagnetic inductive head and has an advantage in that an adequate read output is ensured even if its recording bit becomes smaller and its leakage flux is reduced. Furthermore, a giant magnetoresistive effect head of a spin valve type having even more improved read-back sensitivity is being developed.
Magnetic recording media currently in use include a Co alloy magnetic layer such as CoNiCr, CoCrTa, CoCrPt, or the like, and a Cr underlayer which controls crystallographic orientation of the magnetic layer. The Co alloy magnetic layer has a hexagonal close-packed (hcp) structure having its c-axis as an axis-of-easy magnetization. When the Co alloy magnetic layer is used as a longitudinal magnetic recording media, it is preferable for its c-axis to be oriented in-plane, also referred to as horizontally. Therefore, a method for orientating the c-axis in the direction within the plane is used, whereby a Cr underlayer having a body-centered cubic (bcc) structure is formed on a substrate, then a Co alloy magnetic layer is formed epitaxially thereon so as to orientate the c-axis in-plane.
In the case where a CoCrPt alloy having a large lattice constant is used as a magnetic layer, as disclosed in JP-A Laid-Open Nos. 62-257618 and 63-197018, a lattice spacing is increased by the addition of Ti or V to Cr to improve lattice matching with the magnetic layer so as to more effectively orientate the c-axis in-plane.
When the magnetoresistive head is used during read-back, since noise accompanies the signal being reproduced from the longitudinal magnetic recording media at high sensitivity, significantly improved noise reduction is required for the longitudinal magnetic recording media. The noise is mainly caused from magnetization distortion in a magnetization transition region between recording bits. Therefore, narrowing of this region will lead to a reduction of noise. In order to accomplish this, it is effective to make magnetic crystal grains finer as well as weakening the interaction between respective grains, thereby reducing the size of magnetization reversal. As described above, since there is an epitaxial relationship between the magnetic layer and its underlayer, finer magnetic crystal grains can be obtained by forming crystal grains of the underlayer of a smaller size. In order to form grains of the underlayer of a smaller size, various methods are being studied, but no suitable solution had been discovered until the present invention.